Internet scammers are trying to trick taxpayers into giving away their bank details after it was revealed that millions are in line for a rebate.
Six million people are set to receive a windfall of around £300 as HM Revenue and Customs (HMRC) clears a Pay As You Earn (PAYE) backlog.
Emails claiming to be from HMRC were circulating this week, telling recipients they were in line for a payout and inviting them to enter their personal details.
But HMRC said it would never contact those who are owed money in this way.
A spokeswoman for HMRC said: “We only ever contact customers who are due a tax refund in writing by post.
“We currently don’t use telephone calls, emails or external companies in these circumstances.
“If anyone receives an email claiming to be from HMRC, please send it to email@example.com before deleting it permanently.”
She added: “HMRC will do everything possible to ensure those receiving this email know what steps to take to protect their information, and we are working closely with other law enforcement agencies to target the criminals behind this serious crime and see them brought to justice.”